The continuous production of synthetic resin sheet is disclosed by the following U.S. patents:
Kato et al U.S. Pat. Nos. 3,872,197 and 3,988,098 which disclose the construction and operation of a continuous casting machine, which when fed with a polymerizable syrup, continuously produces a traveling strip of polymerized synthetic resin.
Kato U.S. Pat. No. 3,894,826 which discloses an improvement detail for the above machine.
Kato U.S. Pat. Nos. 3,966,693, 3,999,686 and 4,077,755 which disclose the preparation of the syrup used by the machine.
Kato U.S. Pat. Nos. 3,892,153, 4,009,628 and 4,044,639 which disclose the cutting of the continously produced traveling strip, into commercial lengths.
The disclosures of the above patents are incorporated by reference into the present disclosure. Other continuous casting means and methods may be applicable.
To summarize the general principles of the continuous casting of synthetic resin material, a polymerizable syrup of suitable viscosity is used as a starting material. One example might be methyl methacrylate provided with the suitable viscosity by being partially polymerized to form a monomer-polymer mixture, the methyl methacrylate possibly including a copolymerizable unsaturated monomer. Other polymerizable syrups can be used.
This syrup is fed into the entrance end of the casting and polymerizable space of a continuous casting machine, this space being formed by upper and lower traveling spans of highly polished metal belts. Heated water is sprayed on the outsides of the belt spans to form a first polymerization zone where the syrup is polymerized to a degree making it substantially solid, this first zone being followed by a second polymerization zone where by radiant heat on the outsides of the spans said solid from the syrup is heated to a higher temperature effecting a substantially complete polymerization, after which the spans travel through a cooling zone with the finished strip of material exiting from there as a continuously traveling strip of synthetic resin material having highly polished surfaces imparted by contact with the polished steel belt spans. This strip is then cut into sheets of desired lengths.
For a more detailed understanding of the casting technique, reference may be made to the Kato et al patents, keeping in mind that in this instance the spans are uniquely horizontal throughout with the upper belt span in the first zone held up against gravity by the hydraulic pressure of the syrup resulting from its being fed into the entrance end of the belt spans traveling at a velocity providing this pressure. Synthetic resin strip is also produced by continuous machines which provide a hydrostatic pressure by the belt spans being inclined to degrees causing gravity to produce the pressure.
Such continuously produced strip can be colored by incorporating colorants into the syrup fed to the machine. However, it has proven desirable to provide the strip with a more artistic appearance, for example, such as can be provided potentially by the printing art. The finally cut sheets of the strip material are per se hard-surfaced, resistant to surface marking and substantially weatherproof, characteristics which, however, are not enjoyed by printing applied to the surface of the sheet material.
In the case of the glass cell casting and polymerizing practice, it has been proposed to place a possibly printed film on the inside of one of the cell glass plates prior to casting the syrup into the cell. An example is provided by British Pat. No. 1,274,516. Such practice has resulted in formation of wrinkles in the film. In any event, the glass cell method is necessarily a batch-type operation involving a low production rate and high labor cost.